The effect of photoperiod on the reproductive development of the northern bay scallop, Argopecten irradians irradians

One-year-old bay scallops, Argopecten irradians irradians (58 ± 2 mm, 22 ± 1 g live weight) were exposed to four replicated photoperiod treatments (24D, 8L:16D, 16L:8D, and 24L where D = dark hours, L = light hours) in order to measure the effect on gonad weight and maturation during the conditioning process. Results indicated that day-lengths of more than 8 h are necessary to promote gonad maturation in bay scallops. After 6 wk, the mean gonad weight for scallops in the 16-h and 24-h light regimes was similar at 0.6 ± 0.1 g dry weight compared to a mean of 0.2 ± 0.1 g dry weight for those in the 8-h and 0-h light regimes. Histological assessment indicated significantly more follicular tissue development in both the male and female portion of the gonad in the two longer photoperiod treatments. Overall, gamete maturity was highest for the scallops in the 16-h light regime; the incidence of mature eggs was 50% compared to 35% in the 24-h light regime, 20% in the 8-h light regime and 10% in the 0-h light regime. Assessment of feeding rates indicated no significant difference in algal cell consumption among treatments. Total dry tissue weight doubled over the 6-wk conditioning trial with no significant differences among treatments. One-year-old bay scallops appear to be non-responsive to conditions suitable for gonad maturation (i.e. appropriate temperature and food levels) unless they receive more than 8 h of light exposure. This finding has important implications for northern hatcheries which typically condition broodstock indoors during the early spring.